Method, System and Device for Switching a Transmission Time Interval

ABSTRACT

A method and system for synchronized switching of a Transmission Time Interval (TTI) between at least two different TTI length values. A UE transmitting a power report, where a control node or a Base Station evaluates the report and decides, based on the evaluation, to order the UE to switch to a different TTI length. The order message comprises the number of TTIs after which a TTI switch has to occur, composed a.o. based on radio environment condition. The UE receives a TTI switch order message and replies with a single message to its serving BS with a message to switch the TTI in a synchronous way.

TECHNICAL FIELD

The present invention relates generally to a method, system and deviceto enable synchronized switching between different transmission timeintervals in a wireless communication system.

BACKGROUND

In a typical cellular network, also referred to as a wirelesscommunication system, User Equipments (UEs), communicate via a RadioAccess Network (RAN) to one or more core networks (CNs).

A user equipment is a mobile terminal by which a subscriber can accessservices offered by an operator's core network. The user equipments maybe for example communication devices such as mobile telephones, cellulartelephones, laptops or tablet computers, sometimes referred to as surfplates, with wireless capability. The user equipments may be portable,pocket-storable, hand-held, computer-comprised, or vehicle-mountedmobile devices, enabled to communicate voice and/or data, via the radioaccess network, with another entity, such as another mobile station or aserver.

User equipments are enabled to communicate wirelessly in the cellularnetwork. The communication may be performed e.g. between two userequipments, between a user equipment and a regular telephone and/orbetween the user equipment and a server via the radio access network andpossibly one or more core networks, comprised within the cellularnetwork.

The cellular network covers a geographical area which is divided intocell areas. Each cell area is served by a Base Station, BS, or RadioBase Station (RBS), which sometimes may be referred to as e.g. “eNB”,“eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station),depending on the technology and terminology used.

The base stations may be of different classes such as e.g. macro eNodeB,home eNodeB or pico base station, based on transmission power andthereby also on cell size.

A cell is the geographical area where radio coverage is provided by thebase station at a base station site. One base station, situated on thebase station site, may serve one or several cells. Further, each basestation may support one or several communication technologies. The basestations communicate over the air interface operating on radiofrequencies with the user equipments within range of the base stations.

In some radio access networks, several base stations may be connected,e.g. by landlines or microwave, to a radio network controller, e.g. aRadio Network Controller (RNC) in Universal Mobile TelecommunicationsSystem (UMTS), and/or to each other. The radio network controller, alsosometimes termed a Base Station Controller (BSC) e.g. in GSM, maysupervise and coordinate various activities of the plural base stationsconnected thereto. GSM is an abbreviation for Global System for MobileCommunications (originally: Groupe Special Mobile).

In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE),base stations, which may be referred to as eNodeBs or eNBs, may bedirectly connected to one or more core networks.

UMTS is a third generation (3G) mobile communication system, whichevolved from the second generation (2G) mobile communication system(GSM) and is intended to provide improved mobile communication servicesbased on Wideband Code Division Multiple Access (WCDMA) accesstechnology. UMTS Terrestrial Radio Access Network (UTRAN) is essentiallya radio access network using wideband code division multiple access foruser equipments. The 3GPP has undertaken to evolve further the UTRAN andGSM based radio access network technologies.

In the context of this disclosure, a base station or radio base stationas described above will be referred to as a Base Station (BS). A userequipment as described above, will in this disclosure be referred to asa User Equipment or a UE.

The expression DownLink (DL) will be used for the transmission path fromthe base station to the user equipment. The expression UpLink (UL) willbe used for the transmission path in the opposite direction i.e. fromthe user equipment to the base station.

Cellular communication networks evolve towards higher data rates,together with improved capacity and coverage. In 3GPP, standardizationbody technologies like GSM, HSPA and LTE have been and are currentlydeveloped.

To provide for mobility in the cellular network, the cellular networkmust perform so called handovers when the user equipment moves from onecell to another. A handover means that there is a change of serving cellfor the user equipment from a so-called source cell to a so-calledtarget cell. There are mechanisms in the cellular network to identifywhich cells are candidate target cells for handover. Typically, the userequipment regularly performs measurements to monitor which cells providecoverage at its current location. The measurement result is sent to aserving base station of the source cell in so called measurementreports. These measurement reports may be used to trigger a handover tothe target cell in due time before the user equipment moves out ofcoverage from the source cell.

Apart from handovers, measurements are also made by the UE to enable abase station or control node to decide on the length of the TransmissionTime Interval (TTI) to be deployed. The length of the TTI influences theperformance of the radio communication between UE and BS. A relativelylong TTI length has the advantages of being efficient in errorcorrection and consuming relatively low power, while a relatively shortTTI length has the advantages of providing higher data rates andenabling faster adaptation to a changing radio environment.

When a UE is close to the center of the serving cell, so in generalclose or in short range to the serving BS antenna, a relatively shortTTI is applied. When however the UE is moving away from the center ofthe served cell, the disadvantage occurs that due to the distance thepower required to maintain the BS-UE radio link has to be increased.Increasing power has a disadvantageous effect to other UEs in the samecell and should be limited in order to maintain the radio links betweenthe other UEs and the BS. When reaching this limit, an alternative canbe applied to maintain said BS-UE radio link in deploying a lower powerscheme by switching to a longer TTI.

The actual deployment of either the shorter or longer TTI length is atradeoff between a.o. the parameters listed above

For supporting mobile broadband services, good latency is essential inproviding good end-user experience. This requires short round-trip timeenabled by relatively short TTI.

For the Enhanced UpLink, EUL, the value used for a short TTI istherefore preferred over the long TTI. In current 3G networks, there isstill a substantial amount of large macro cells where supporting theshort TTI in the entire cell may be a challenge. In such environments,it may be necessary to apply to the long TTI for a UE residing at thecell boundary.

A problem is that, the BS and the UE should switch to a different TTI,listed as a TTI switching process, at the same instant, and it isregarded that this is a process of that takes time and takes power, e.gpower from the battery fed UE, causing the TTI switching processreducing available lifetime of the operational up-time of the UE.

Another problem is that the TTI switching process requires signalingthat is applied via the radio environment, thereby competing with, or atleast influencing or interfering, other UEs for radio links with the BS,and can be disadvantageously influenced by changing radio environmentconditions, which may result in an unsatisfactory TTI switching process.Failed transmissions of data after an unsatisfying TTI switch may occur.

SUMMARY

In view of the discussion above, it is an object for embodiments hereinto provide an improved and robust way of performing TTI switching in acellular network.

In particular, it is an object for embodiments to increase the chancesto correctly perform a TTI switching procedure.

In an aspect of the invention a method for synchronized switching of aTransmission Time Interval, TTI, between at least two different TTIlength values is proposed, wherein the method is performed by a numberof steps described below.

In a first step a User Equipment (UE) transmits a report comprising ameasured received power by the UE.

In a second step a Base Station (BS) being the serving BS for the UE,receives the report, and forwards the report to a Control Node.

In a further step the Control Node receives the report, evaluates thereport and decides, based on the evaluation, to order the UE toinitialize a switching of an actual TTI length value to a different TTIlength value, by transmitting a switching message, the switching messagecomprising a first identifier identifying the different TTI lengthvalue.

In a still further step the BS receives the switching message, andforwards the switching message to the UE.

In a still further step the UE transmits a single reply message inresponse to receiving the switching message, for acknowledging receptionof the switching message and initializes a synchronized switching to thedifferent TTI length value identified by the first identifier.

In a further aspect of the invention a method in a User Equipment UE,for synchronized switching of a Transmission Time Interval (TTI) betweenat least two different TTI length values, the UE deploying an actual TTIlength value, is proposed, wherein the method is performed by a numberof steps described below.

In a first step the UE receives a switching message comprising a firstidentifier identifying a different TTI length value.

In a second step the UE transmits a single reply message in response tothe switching message, for acknowledging reception of the switchingmessage and initializing a synchronized switching to the different TTIlength value identified by the first identifier.

In a still further aspect of the invention a method in a Base Station,BS, for synchronized switching of a Transmission Time Interval, TTI,between at least two different TTI length values, is proposed whereinthe BS deploys an actual TTI length value, and wherein the method isperformed by a number of steps described below.

In a first step the BS receives a report comprising a measured receivedpower by a User Equipment, UE, and forwards the report.

In a second step the BS, receiving a switching message in response tothe forwarded report, and forwards the switching message, wherein theswitching message comprises a first identifier identifying a differentTTI length value.

In a further step the BS receives a single reply message in response totransmitting the switching message, for acknowledging reception of theswitching message and initializing a synchronized switching to thedifferent TTI length value identified by the first identifier.

In a still further step the BS holds transmission of messages for anumber of TTIs, and in a still further step the BS commencestransmission of messages deploying the different TTI length value.

In a still further aspect of the invention a method in a Base Station,BS, for synchronized switching of a Transmission Time Interval, TTI,between at least two different TTI length values, is proposed whereinthe BS deploys an actual TTI length value, and wherein the method isperformed by a number of steps described below.

In a first step the BS receives a report comprising a measured receivedpower by a User Equipment, UE.

In a second step the BS evaluates the report and decides, based on theevaluation, to order the UE to initialize a switching of an actual TTIlength value to a different TTI length value, by transmission of aswitching message, wherein the switching message comprises a firstidentifier identifying a different TTI length value.

In a further step the BS receives a single reply message in response tothe transmission of the switching message, for acknowledging receptionof the switching message and initializing a synchronized switching tothe different TTI length value identified by the first identifier.

In a still further step the BS holds its transmission of messages for anumber of TTIs and,

In a still further step the BS commences the transmission of messagesdeploying the different TTI length value.

In a still further aspect of the invention a system in for synchronizedswitching of a Transmission Time Interval, TTI, between at least twodifferent TTI length values, is proposed, wherein the system comprisesat least one User Equipment, UE, at least one Base Station, BS, and aControl Node.

The UE of the system is arranged to transmit a report comprising ameasured received power by the UE;

The BS comprised by the system, being the serving BS of UE, is arrangedto receive the report, and forward the report to the Control Node.

The Control Node comprised by the system is arranged to receive thereport, evaluate the report and decide, based on the evaluation, toorder the UE to initialize a switch of an actual TTI length value to adifferent TTI length value, wherein the control node is further arrangedto transmit a switching message, wherein the switching message comprisesa first identifier identifying a different TTI length value.

The BS is further arranged to receive the switching message, and toforward the switching message.

The UE is further arranged to transmit a single reply message inresponse to the reception of the switching message, for anacknowledgement of reception of the switching message, and to initializea synchronized switching to the different TTI length value identified bythe first identifier.

In a still further aspect of the invention a User Equipment, UE, forsynchronized switching of a Transmission Time Interval, TTI, between atleast two different TTI length values, is proposed wherein the UE isarranged to deploy an actual- and a different-TTI length value.

The UE comprises a processing unit arranged to process programinstructions.

The UE further comprises a memory arranged to store the programinstructions and network parameters

The UE still further comprises an interface arranged to connect to otherentities, and wherein the processing unit is further arranged, under theprogram instructions, to control the interface, in that a switchingmessage comprising a first identifier identifying the different TTIlength value is received and stored in the memory.

The processing unit comprised by the UE is further arranged, under theprogram instructions to compile a single reply message in response tothe switching message, as to acknowledge reception of the switchingmessage and as to initialize a synchronized switching to the differentTTI length value identified by the first identifier.

The processing unit comprised by the UE still further arranged, underthe program instructions to control the interface to transmit thecompiled single reply message.

In a still further aspect of the invention a Base Station, BS, forsynchronized switching of a Transmission Time Interval, TTI, between atleast two different TTI length values, is proposed wherein the BS isarranged to deploy an actual- and a different-TTI length value.

The BS comprises a processing unit arranged to process programinstructions.

The BS further comprises a memory arranged to store the programinstructions and network parameters.

The BS still comprising an interface arranged to connect to otherentities, and wherein

the processing unit is further arranged, under the program instructions,to control the interface, in that a report message is received, andwherein the report message comprises a report comprising a measuredreceived power by a User Equipment, UE, which is forwarded.

The processing unit comprised by the BS, is further arranged, under theprogram instructions, to control the interface, in that a switchingmessage is received in response to the forwarded report.

The processing unit comprised by the BS, is still further arranged,under the program instructions, to control the interface by forwardingthe switching message, wherein the switching message comprises a firstidentifier identifying the different TTI length value.

The processing unit comprised by the BS is still further arranged, underthe program instructions, to control the interface, in that a singlereply message is received and forwarded, wherein the single replymessage is interpreted by the processing unit as an acknowledge to theswitching message transmission and the single reply message interpretedby the processor as an initiation to hold transmissions with respect tothe UE.

In a still further aspect of the invention a Base Station, BS, forsynchronized switching of a Transmission Time Interval, TTI, between atleast two different TTI length values, is proposed, wherein the BS isarranged to deploy an actual- and a different-TTI length value.

The BS comprises a processing unit arranged to process programinstructions;

The BS further comprises a memory arranged to store the programinstructions and network parameters;

The BS still further comprises an interface arranged to connect to otherentities, and wherein

the processing unit is further arranged, under the program instructions,to control the interface, in that a report message is received, whereinthe report message comprises a report comprising a measured receivedpower by a User Equipment, UE.

The processing unit comprised by the BS is still further arranged, underthe program instructions, to evaluate the report and to deciding, basedon the evaluation, to order the UE to initialize a switching of anactual TTI length value to a different TTI length value, and to transmita switching message, wherein the switching message comprises a firstidentifier identifying the different TTI length value.

The processing unit comprised by the BS still further arranged, underthe program instructions, to control the interface, in that a singlereply message is received and forwarded, wherein the single replymessage is interpreted by the processing unit as an acknowledge to theswitching message transmission and wherein the single reply message isinterpreted by the processor as an initiation to hold transmissions withrespect to the UE.

In a still further aspect of the invention a computer program isproposed, which, when being executed by a processing unit in a UserEquipment, UE, is adapted to carry out or control a method forsynchronized switching of a Transmission Time Interval, TTI, between atleast two different TTI length values, wherein the UE further adapted todeploy an actual- and a different-TTI length value, and wherein thecomputer program performs the steps listed below.

As a first step the UE receives a switching message comprising a firstidentifier identifying the different TTI length value.

As a second step the UE transmits a single reply message in response tothe switching message, for acknowledging the reception of the switchingmessage and initializes a synchronized switching to the different TTIlength value identified by the first identifier.

In a still further aspect of the invention a computer program isproposed which, when being executed by a processing unit in a BaseStation, BS, is adapted to carry out or control a method forsynchronized switching of a Transmission Time Interval, TTI, between atleast two different TTI length values, the BS further adapted to deployan actual- and a different-TTI length value, and wherein the computerprogram performs the steps listed below.

As a first step the BS receives a report comprising a measured receivedpower by a User Equipment, UE, and wherein the report is forwarded.

As a second step the BS receives a switching message in response to theforwarded report, and wherein the switching message is forwarded,wherein the switching message comprising a first identifier identifyinga different TTI length value.

As a further step the BS receives a single reply message in response tothe transmission of the switching message, for acknowledging receptionof the switching message and initializing a synchronized switching tothe different TTI length value identified by the first identifier.

As a still further step the BS holds the transmission of messages for anumber of TTIs.

As a still further step the BS commences transmission of messages thatdeploy the different TTI length value.

In a still further aspect of the invention a computer program isproposed, which, when being executed by a processing unit in a BaseStation, BS, is adapted to carry out or control a method forsynchronized switching of a Transmission Time Interval, TTI, between atleast two different TTI length values, the BS further adapted to deployan actual- and a different-TTI length value, and wherein the computerprogram performs the steps listed below.

As a first step the BS receives a report comprising a measured receivedpower by a User Equipment, UE.

As a second step the BS evaluates the report and decides, based on theevaluation, to order the UE to initialize a switching of an actual TTIlength value to a different TTI length value, by transmission of aswitching message, wherein the switching message comprises a firstidentifier identifying a different TTI length value.

As a further step the BS receives a single reply message in response tothe transmission of the switching message, for acknowledging receptionof the switching message and initializing a synchronized switching tothe different TTI length value identified by the first identifier.

As a still further step the BS holds the transmission of messages for anumber of TTIs.

As a still further step the BS commences the transmission of messagesdeploying the different TTI length value.

In a still further aspect of the invention an apparatus for synchronizedswitching of a Transmission Time Interval, TTI, between at least twodifferent TTI length values, is proposed wherein the apparatus isarranged to deploy an actual- and a different-TTI length value.

The apparatus comprises an Input/Output, I/O, module for receiving aswitching message. The switching message comprises a first identifieridentifying the different TTI length value and a second identifieridentifying a number of TTIs after which a switching of a current TTIlength value to the different TTI length value has to occur.

The apparatus further comprises a storage module for storing the firstand the second identifier

the I/O module comprised by the apparatus additionally applied fortransmitting a single reply message in response to the switchingmessage, as to acknowledge reception of the switching message and as toinitialize a synchronized switching to the different TTI length valueidentified by the first identifier.

The apparatus still further comprising a counter module to startcounting the number of TTIs on transmission of the single reply messagethe number of TTIs until the value indicated by the second identifier.

The apparatus still further comprising a hold transmission module tohold transmission of messages via the I/O module during counting of thecounter module.

These and other embodiments according to the present invention are nowillustrated in more detail with reference to the enclosed drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an embodiment of a system;

FIG. 2 is a signaling diagram illustrating an embodiment of methodsteps;

FIG. 3 is a signaling diagram illustrating an embodiment of methodsteps;

FIG. 4 is a block diagram illustrating an embodiment of a device;

FIG. 5 is a block diagram illustrating an embodiment of a device;

DETAILED DESCRIPTION

FIG. 1 is a block diagram illustrating an embodiment of a system.

FIG. 1 shows an arbitrary number of three Base Stations (BS), 110, 120,130, each having a coverage area, also known as cell. The coverage areaof BS 110 is referenced 115B. The other BSs 120, 130 have identicalcoverage areas. A BS might be as an example a Base Transceiver Station,BTS, Node B or enhanced Node-B, eNode-B

As illustrated above there is a region in the BS coverage area where arelatively short Transmission Time Interval, TTI, referenced as shortTTI, is applied and a region where a relatively long TTI, referenced aslong TTI, is applied.

For BS 110 the area comprised by circle 115A is illustrativelydesignating the area applying a short TTI and the area between circles115A and circle 115B is illustratively designated the area for applyingthe long TTI. The other BS 120 and 130 have identical areas within thecoverage area.

The BS 110 is the serving BS for User Equipment (UE) 100, residing inthe coverage area 115B of BS 110. The BS 120 and 130 are referenced asnon-serving BS, but are potential serving BSs if UE 100 moves to theirrespective coverage areas.

The BSs 110, 120, 130 are linked to a control node 150, which might beas an example a Base Station Controller, BSC, a Radio NetworkController, RNC. The links enable communication between the BSs and theControl Node 150 wherein the Control Node is enabled to forward messagesbetween the BSs.

The switching procedure needs to be synchronized in order for the UE andthe network to know when the TTI switching takes place. As in anysynchronized procedure, there is a risk associated with the execution,in particular in situations where coverage is an issue.

FIG. 2 is a signaling diagram illustrating an embodiment of methodsteps.

FIG. 2 presents the signaling between the UE 100, the serving BS 110,the non-serving BS 120, 130 and the Control Node 150. FIG. 2 representsan embodiment wherein the control node 150 decides on a TTI switch.

It is to be understood that a number of network parameters, such asapplicable TTI value lengths, an applicable number of TTIs after which aswitching of the actual TTI length value to a different TTI length thanthe actual TTI length, has to occur, are exchanged in an initial stagebetween UE 100, BS 110, 120, 130 and optionally the Control Node, suchthat an indicator can be applied in messages, referring to thepredetermined exchanged parameter. As an example, the short TTI and longTTI length are already exchanged as 2 ms and 10 ms and stored in UE 100and BSs 110, 120, 130.

The UE 100, transmits 210 a report comprising a measured received powerby the UE 100. This report is e.g a filtered Uplink Power Headroom, UPH,18-bit Protocol Data Unit (PDU) message. The report is transmittedperiodically, when the UE is triggered by changing radio environmentconditions or when the serving BS requests for a report.

The serving BS 110, receives 220 the report, and forwards 225 the reportto the Control Node 150.

The Control Node 150 receives 230 the report and evaluates 232 thereport.

the TTI switching decision is based in an evaluation of a Media AccessControl (MAC) Uplink Power Headroom (UPH) report transmitted by the UE.The values of the short TTI 2 ms and the long TTI 10 ms TTI length arepre-configured in the UE and the BS.

The UE sends an 18-bit UPH report to the serving BS when triggeringcriteria are met or periodically.

Both the UE and the BS will switch to a different TTI length, apredefined number of TTIs after the completion of the synchronizedreconfiguration.

The Control Node 150 decides, based on the evaluation, to order the UE100 to initialize a switching of an actual TTI length value to adifferent TTI length value, by transmitting 234 a switching message, theswitching message comprising a first identifier identifying thedifferent TTI length value. The synchronized reconfiguration of BS andUE, is achieved by using a High Speed Shared Control Channel, HS-SCCHorder message, followed by a L1 acknowledge, ACK in response to theHS-SCCH order message.

The TTI switch is, depending on the actual TTI length a switch toanother TTI length. In case there are only two TTI lengths arepredefined, a toggle between both is applicable. In case more than twoTTI lengths are predefined the first identifier identifies which one TTIlength. As an example, 2 ms and 10 ms TTI length are listed although asan example a range of values such as 0.1, 0.2, 0.4, 0.5, 0.8, 1, 1.2,1.5 ms for the short TTI and 1, 2, 4, 6, 8, 10 ms for the long TTI areapplicable as long as there is a difference between both TTIs.

The Control Node 150 is, apart from deciding whether a TTI switch has tooccur, also decisive in the number of TTI which has to be deployed afterwhen a TTI switch occurs. E.g. the actual radio environment conditionsinfluence the selected TTI number value.

The serving BS 110 receives 240 the switching message, and forwards 245the switching message to the UE 100. The switching message 245 is amessage such as a High Speed-Shared Control Channel HS-SCCH message.

The UE 100 transmits 255 a single reply message in response to receiving250 the switching message, for acknowledging reception of the switchingmessage and initializing a synchronized switching to the different TTIlength value identified by the first identifier. The single replymessage is a TTI switch commit message e.g. a High Speed-DedicatedPhysical Control Channel (HS-DPCCH) message as an 18 bit Protocol DataUnit (PDU) message.

The serving BS 110, forwards 265 the single reply message to the ControlNode 150, as to enable other BSs, e.g. the non-serving BS 120, 130, toalso be aware that the TTI for UE 100 has changed. The single replymessage sent by the serving BS 110 is a TTI length update message.

The Control Node 150 receives 270 the single reply message and inresponse transmits 275 a second message to non serving Base Stations120, 130 for synchronized switching to the different TTI length valueidentified by the first identifier, the second message additionallycomprising a second identifier identifying a number of TTIs after whicha switching of the actual TTI length value to the different TTI lengthhas to occur. The single reply message comprises also the indicatorindicating the different TTI length value, such that when thetransmission from the serving BS 110 via the Control Node 150 towardsthe non-serving BSs 120, 130, takes longer than the TTI switchingprocedure, due to network latency, are still aware of the different TTIlength value of the UE 100. The second message transmitted 275 by theControl node is a TTI length update message.

The UE 100 holds 280 transmission of messages for a number of TTIs equalto the number of TTIs identified by the second identifier and theserving BS 110 receiving 260 the single reply message holds transmissionof messages in relation to the UE 100 for a number of TTIs equal or inrelation to the number of TTIs identified by the second identifier.

The UE 100 and the serving BS 110 commence 290 transmissions of messagesdeploying the different TTI length value.

Depending on the configuration of the serving BS 110 and UE 100, thenumber of Ills identified by the second identifier is decreased by e.g.a configurable fixed value of 0, 1, 2 or 3, as to enable the serving BS110 to synchronize the TTI switch initialised by the UE 100, between theUE 100 and the serving BS 110.

Optionally the UE 100 transmits a reply Acknowledge message 255A inresponse to receiving 250 of the switching order message, replacing theacknowledgement in the single reply message. The serving BS 110 receives260A the Acknowledge and starts waiting for the single reply message 260as to initiate the TTI switching.

In case of a potential Soft Handover, i.e. a UE in idle mode changing aserving cell, in order to ensure that both serving and non-serving BSsperform a TTI switch simultaneously, the UE sends a L1 or MAC indicationafter receiving the HS-SCCH order before the actual switch.Alternatively, the serving BS informs the Control Node of the TTI lengthupdate and the Control Node forwards the information to all the BSs inorder to guarantee the alignment among serving and non-serving BS.

FIG. 3 is a signaling diagram illustrating an embodiment of methodsteps.

FIG. 3 presents the signaling between the UE 100, the serving BS 110A,the non-serving BS 120, 130 and the Control Node 150. FIG. 2 representsan embodiment wherein the serving BS 110A decides on a TTI switch.

It is to be understood that a number of network parameters, such asapplicable TTI value lengths, an applicable number of Ills after which aswitching of the actual TTI length value to a different TTI length thanthe actual TTI length, has to occur, are exchanged in an initial stagebetween UE 100, BS 110A, 120, 130 and optionally the Control Node, suchthat an indicator can be applied in messages, referring to thepredetermined exchanged parameter. As an example the short TTI and longTTI length are already exchanged as 2 ms and 10 ms and stored in UE 100and BSs 110A, 120, 130.

The UE 100, transmits 510 a report comprising a measured received powerby the UE 100. This report is e.g a filtered Uplink Power Headroom, UPH,18 bit Protocol Data Unit (PDU) message. The report is transmittedperiodically, when the UE is triggered by changing radio environmentconditions or when the serving BS requests for a report.

The serving BS 110A, receives 520 the report and evaluates 521A thereport.

the TTI switching decision is based in an evaluation of a Media AccessControl Uplink Power Headroom, MAC UPH, report transmitted by the UE.The values of the short TTI 2 ms and the long TTI 10 ms TTI length arepre-configured in the UE and the BS.

The UE sends an 18-bit UPH report to the serving BS when triggeringcriteria are met or periodically.

Both the UE and the BS will switch to a different TTI length, apredefined number of TTIs after the completion of the synchronizedreconfiguration.

The serving BS 110A decides, based on the evaluation, to order the UE100 to initialize a switching of an actual TTI length value to adifferent TTI length value, by transmitting 545 a switching message tothe UE 100. The switching message 545 is a message such as a HighSpeed-Shared Control Channel HS-SCCH message.

The synchronized reconfiguration of BS and UE, is achieved by using aHigh Speed Shared Control Channel, HS-SCCH order message, followed by aL1 acknowledge, ACK in response to the HS-SCCH order message.

The switching message comprising a first identifier identifying thedifferent TTI length value. The TTI switch is, depending on the actualTTI length a switch to another TTI length. In case there are only twoTTI lengths are predefined, a toggle between both is applicable. In casemore than two TTI lengths are predefined the first identifier identifieswhich one TTI length. As an example, 2 ms and 10 ms TTI length arelisted although as an example a range of values such as 0.1, 0.2, 0.4,0.5, 0.8, 1, 1.2, 1.5 ms for the short TTI and 1, 2, 4, 6, 8, 10 ms forthe long TTI are applicable as long as there is a difference betweenboth TTIs.

The BS 110A is, apart from deciding whether a TTI switch has to occur,also decisive in the number of TTI which has to be deployed after when aTTI switch occurs. E.g. the actual radio environment conditionsinfluence the selected TTI number value.

The UE 100 transmits 555 a single reply message in response to receiving550 the switching message, for acknowledging reception of the switchingmessage and initializing a synchronized switching to the different TTIlength value identified by the first identifier. The single replymessage is a TTI switch commit message e.g. a High Speed-DedicatedPhysical Control Channel (HS-DPCCH) message, as an 18 bit Protocol DataUnit (PDU) message.

The serving BS 110, forwards 565 the single reply message to the ControlNode 150, as to enable other BSs, e.g. the non-serving BS 120, 130, toalso be aware that the TTI for UE 100 has changed. The single replymessage sent by the serving BS 110A is a TTI length update message.

The Control Node 150 receives 570 the single reply message and inresponse transmits 575 a second message to non-serving Base Stations120, 130 for synchronized switching to the different TTI length valueidentified by the first identifier, the second message additionallycomprising a second identifier identifying a number of TTIs after whicha switching of the actual TTI length value to the different TTI lengthhas to occur. The single reply message comprises also the indicatorindicating the different TTI length value, such that when thetransmission from the serving BS 110A via the Control Node 150 towardsthe non-serving BSs 120, 130, takes longer than the TTI switchingprocedure, due to network latency, are still aware of the different TTIlength value of the UE 100. The second message transmitted 575 by theControl node is a TTI length update message.

The UE 100 holds 580 transmission of messages for a number of TTIs equalto the number of TTIs identified by the second identifier and theserving BS 110A receiving 560 the single reply message holdstransmission of messages in relation to the UE 100 for a number of TTIsequal or in relation to the number of TTIs identified by the secondidentifier.

The UE 100 and the serving BS 110A commence 590 transmissions ofmessages deploying the different TTI length value.

Depending on the configuration of the serving BS 110A and UE 100, thenumber of TTIs identified by the second identifier is decreased by e.g.a configurable fixed value of 1, 2 or 3, as to enable the serving BS110A to synchronize the TTI switch initialised by the UE 100, betweenthe UE 100 and the serving BS 110A.

Optionally the UE 100 transmits a reply Acknowledge message 555A inresponse to receiving 550 of the switching order message, replacing theacknowledgement in the single reply message. The serving BS 110Areceives 560A the Acknowledge and starts waiting for the single replymessage 560 as to initiate the TTI switching.

It is applicable to both FIGS. 2 and 3 that the UE 100 does not sendHybrid Automatic Report Requests Acknowledgement (HARQ-ACK) messages inresponse to the HS-SCCH order message, as it saves UE's battery power aswell as reduces interference to other UEs. In addition, once the BS 110,110A sends an order message 245, 545 to switch the TTI either on aprimary or secondary carrier, the BS 110, 110A can switch off thereceiver when decoding the High Speed-Dedicated Physical Control Channel(HS-DPCCH) message in response to this order message (1st slot).

Also with respect to both FIGS. 2 and 3, when the UE 100 is configuredwith multiple carriers in the downlink transmission and if at least twocarriers are activated, then sending the HS-SCCH order message 245, 545from the secondary carrier to inform about the TTI switching has abenefit on the system throughput for downlink.

If e.g. the primary carrier is loaded (general case) and sending anHS-SCCH order message requires certain amount of power (10% of total BS110, 110A power) and the channelization code. In this way, power isreduced.

In general secondary carriers are not that loaded. It is proposed tosend an HS-SCCH order message via the secondary carrier to the UE 100 toinform about the TTI switch

In case of a potential Soft Handover, i.e. a UE in idle mode changing aserving cell, in order to ensure that both serving and non-serving BSsperform a TTI switch simultaneously, the UE sends a L1 or MAC indicationafter receiving the HS-SCCH order before the actual switch.Alternatively, the serving BS informs the Control Node of the TTI lengthupdate and the Control Node forwards the information to all the BSs inorder to guarantee the alignment among serving and non-serving BS.

FIG. 4 is a block diagram illustrating an embodiment of a device.

FIG. 4 is a block diagram illustrating an embodiment of a UE 100arranged for synchronized switching of a Transmission Time Interval,TTI, between at least two different TTI length values. The UE isarranged to deploy an actual- and a different-TTI length value.

The UE 100 comprises:

a processing unit 301 arranged to process program instructions;

a memory 302 arranged to store the program instructions and networkparameters;

an interface, I/O module 303 arranged to connect to other entities.

The processing unit 301, comprises a processor 301A arranged to executefunctional modules TTI counter 310 and Hold module 320.

The processing unit 301 is further arranged, under the programinstructions, to control the interface 303, in that a switching messagecomprising a first identifier identifying the different TTI length valueis received 250, 550 and stored in the memory 302.

The processing unit 301 is further arranged, under the programinstructions to compile a single reply message in response to theswitching message, as to acknowledge reception of the switching messageand as to initialize a synchronized switching to the different TTIlength value identified by the first identifier.

The processing unit 301 is further arranged, under the programinstructions to control the interface 303 to transmit the compiledsingle reply message.

The Interface 303 is further arranged to connect to input devices (notshown), such as a keyboard, touchscreen, microphone, and output devices(not shown) such as a screen or speaker. The interface 303 is furtherarranged to maintain a wireless connection to e.g. a serving BS 110 in acommunications network.

The processing unit 301 of UE 100 is further arranged, under the programinstructions, to control the interface 303, in that the switchingmessage additionally comprises a second identifier identifying a numberof TTIs after which a switching of a current TTI length value to thedifferent TTI length value has to occur, is received, and wherein theprocessing unit 301 is further arranged under the program instructionsto control the interface 303 with holding transmission of messages for anumber of TTIs equal to the number of TTIs identified by the secondidentifier and, commencing transmission of messages deploying thedifferent TTI length value.

The processor 301A of UE 100 is arranged under the program instructionsto control a TTI counter 310 that counts the number of TTIs equal to thenumber of TTIs identified by the second identifier. The processor isfurther arranged to control a hold transmission module 320 to holdtransmission of messages via I/O module 303 during counting of thecounter module 310.

The processing unit 301 of UE 100 is further arranged under the programinstructions to control the interface 303 to transmit an acknowledgement255A, 555A in response to the reception 250, 550 of the switchingmessage, intended for replacing the acknowledgement in the single replymessage.

FIG. 5 is a block diagram illustrating an embodiment of a device.

FIG. 5 is a block diagram illustrating an embodiment of a BS 100, 100Aarranged for synchronized switching of a Transmission Time Interval,TTI, between at least two different TTI length values. The BS isarranged to deploy an actual- and a different-TTI length value.

The BS 110, 110A comprises:

a processing unit 401 arranged to process program instructions;

a memory 402 arranged to store the program instructions and networkparameters;

an interface, I/O module 403 arranged to connect to other entities.

The processing unit 401 is further arranged, under the programinstructions, to control the interface 403, in that a report message isreceived 220, 520, the report message comprising a report comprising ameasured received power by a User Equipment, UE 100 and

The processing unit 401 further arranged, under the programinstructions, to control the interface 403, in that a switching message,in response to the report message, is transmitted 245. The switchingmessage comprises a first identifier identifying the different TTIlength value.

the processing unit 401 is further arranged, under the programinstructions, to control the interface 403, in that a single replymessage is received 260 and forwarded 265, the single reply messageinterpreted by the processing unit 401 as an acknowledge to theswitching message transmission 245 and the single reply message isinterpreted by the processing unit 401 as an initiation to holdtransmissions with respect to the UE 100.

The processing unit 401 of the BS 110, 110A is further arranged, underthe program instructions to control the interface 403 to receive 420 theswitching message wherein the switching message additionally comprises asecond identifier identifying a number of TTIs after which a switchingof the actual TTI length value to the different TTI length has to occur,and wherein the processing unit 401 is further arranged, under theprogram instructions, to control the interface 403 that after reception260, 560 of the single reply message, transmission of messages inrelation to the UE 100 is hold for a number of TTIs equal or in relationto the number of TTIs identified by the second identifier.

The processor 401A of the BS 110, 110A is arranged, under the programinstructions to start a response counter 411 after transmission of theswitching message 245, 545 and to send the switching message again whena predetermined value is reached by the response counter 411.

The processing unit 401 of the BS 110, 110A is further arranged underthe program instructions to control the interface 403 to receive anacknowledgement 260A, 560A in response to the transmission 245, 545 ofthe switching message, replacing the acknowledgement in the single replymessage.

the processor 401A of the BS 110A further arranged, under the programinstructions, to evaluate 521A the received 520 report and deciding,based on the evaluation, to order the UE 100 to initialize a switchingof an actual TTI length value to a different TTI length value, andtransmit 545 a switching message wherein the switching messagecomprising a first identifier identifying the different TTI lengthvalue.

It is proposed to apply the switching message 245, 545 as an ordermessage such as the HS-SCCH order message to inform the UE to performthe TTI switch (2 ms to 10 ms or 10 ms to 2 ms).

If the order message is transmitted from the serving High Speed DownlinkShared Channel (HS-DSCH) cell or a secondary serving HS-DSCH cell, forthis Order type, the meaning of the order message is proposed as listedin the Table X.X below. The Order Mapping valued identifiers Xord,1,Xord,2, Xord,3, have example values in the table X.X. below and shouldbe predefined and in combination identify a particular switch from 2 msTTI to 10 ms TTI or vice versa.

TABLE X.X Orders to inform the UE to perform the TTI switch Extended TTIswitch Order A = TTI switch from Type Order Type 2 ms to 10 ms order; B= X_(eodt,1), X_(odt,1), Order Mapping TTI switch from X_(eodt,2)X_(odt,2), X_(odt,3) X_(ord,1) X_(ord,2) X_(ord,3) 10 ms to 2 ms order11 011 1 1 1 A 0 0 0 B 0 0 1 Unused (Reserved) 0 1 0 Unused (Reserved) 01 1 Unused (Reserved) 1 0 0 Unused (Reserved) 1 0 1 Unused (Reserved) 11 0 Unused (Reserved)

In general, the Control Node 150, or the BS 110A configures the value‘N’, where N is the number of Ills after which the UE 100 should switch.

In a further example embodiment, it is proposed that the BS 100, 110Acan set (change) the value of N and indicate this in the HS-SCCH ordermessage 245, 545.

In the example below, N is indicated by N1, N2, N3 and N4. Thereby theHS-SCCH order message indicates the value of N as shown in Table below

Depending on the configuration of the serving BS 110, 110A and UE 100,the number of TTIs identified by the second identifier is decreased bye.g. a configurable fixed value for N of 0, 1, 2 or 3, representing N1,N2, N3 or N4 respectively, as to enable the serving BS 110 tosynchronize the TTI switch initialised by the UE 100, between the UE 100and the serving BS 110.

It is proposed to further adapt table X.X into table Y.Y as shown belowas to deploy the idea of synchronized TTI switching as presented.

TABLE Y.Y Orders to inform the UE to perform the TTI switch Extended TTIswitch Order A = TTI switch from Type Order Type 2 ms to 10 ms order; B= X_(eodt,1), X_(odt,1), Order Mapping TTI switch from X_(eodt,2)X_(odt,2), X_(odt,3) X_(ord,1) X_(ord,2) X_(ord,3) 10 ms to 2 ms order11 011 1 1 1 A with N = N1 0 0 0 B with N = N1 0 0 1 A with N = N2 0 1 0B with N = N2 0 1 1 A with N = N3 1 0 0 B with N = N3 1 0 1 A with N =N4 1 1 0 B with N = N4

The method and devices presented advantageously provide an efficient TTIswitching process where the UE 100 does not need to send an Acknowledgeto the BS 110, 110A, because the UE 100 will send the TTI switch commit(18 bit PDU) 255, 555 to the serving BS 110, 110A, thereby achieving therequired synchronization and preserving an acknowledgement message,resulting into saving UE battery power, and interference with othertransmissions.

The method and devices presented advantageously provide the possibility,when the UE 100 is configured with multiple carriers in the downlink,and the if at least 2 carriers are activated, to send the HS-SCCH 245,545 switching order message from the secondary carrier in order toinform about the TTI switching thereby increasing the chance on asuccessful TTI switch.

The method and devices presented advantageously provide the BS 110, 110Amay go into Discontinuous Reception (DRX) after sending the HS-SCCH 245,545 switching order message, for the HARQ-ACK for this order, therebysaving power.

The suggested process enables the switch to the long TTI as late aspossible in order to retain the advantage of the short TTI (e.g. forhigh data rates) and to avoid back-and-forth reconfigurations

An efficient short TTI 2 ms to long 10 ms TTI switch is directly relatedto the accuracy of the coverage measurement and to the speed androbustness of the switching procedure. In case of non-optimalmeasurement triggers and slow switching procedures, some conservativesafety margins would have to be taken into account (e.g. a longactivation time for the switching procedure, leading to an earlyswitch), resulting in further loss of short TTI 2 ms coverage.

The use of a second identifier has the advantage that the activationtime is set to prevent that when the activation time is not sufficientlylong, it might lead to the situation in which the BS and the UE do notswitch at the same time, remaining misaligned for one or more ConnectionFrame Number (CFN) cycles.

1. A method in a User Equipment (UE) for synchronized switching of aTransmission Time Interval (TTI) between at least two different TTIlengths, the method comprising: receiving a switching message indicatingthat the UE is to switch from using TTIs having a first length to usingTTIs having a second length; and, in response to said switching message,switching from using TTIs having the first length to using TTIs havingthe second length, after a predetermined number of TTIs.
 2. The methodof claim 1, wherein the method further comprises transmitting a reportcomprising a measured received power, and wherein the switching messageis received in response to the report.
 3. The method of claim 1, whereinthe method further comprises, prior to receiving the switching message,receiving a network parameter indicating an applicable number of TTIsafter which a switching of TTI length is to occur, and wherein thepredetermined number of TTIs is the indicated applicable number of TTIs.4. The method of claim 1, wherein the UE is configured with multiplecarriers in the downlink transmission and wherein at least two carriers,a primary and a secondary carrier, are activated, and wherein theswitching message is received by the UE via the secondary carrier. 5.The method of claim 1, wherein the switching message sent by a servingHigh Speed Downlink Shared Channel (HS-DSCH) cell or a secondary servingHS-DSCH cell, comprises a predetermined order mapping indicatorindicating an order for switching a short TTI length to a long TTIlength or vice versa.
 6. The method of claim 1, wherein the methodfurther comprises starting a counter counting TTIs, the value of thecounter indicating when transmission with the second TTI lengthcommences.
 7. A method in a Base Station (BS) for synchronized switchingof a Transmission Time Interval (TTI) between at least two different TTIlength values, the method comprising: receiving, from a User Equipment(UE), a report comprising a measured received power; evaluating thereport and deciding, based on the evaluation, to order the UE toinitialize a switching from a first TTI length to a second TTI length,by transmitting a switching message indicating that the UE is to switchfrom using TTIs having the first length to using TTIs having the secondlength; and, after transmitting the switching message, switching, forcommunications with the UE, from using TTIs having the first length tousing TTIs having the second length, after a predetermined number ofTTIs.
 8. The method of claim 7, wherein the method further comprises,prior to transmitting the switching message, sending, to the UE, anetwork parameter indicating an applicable number of TTIs after which aswitching of TTI length is to occur, and wherein the predeterminednumber of TTIs is the indicated applicable number of TTIs.
 9. The methodof claim 7, wherein the UE is configured with multiple carriers in thedownlink transmission and wherein at least two carriers, a primary and asecondary carrier, are activated, and wherein the switching message issent by the BS via the secondary carrier.
 10. The method of claim 7,wherein the switching message, sent by a serving High Speed DownlinkShared Channel (HS-DSCH) cell or a secondary serving HS-DSCH cell,comprises a predetermined order mapping indicator indicating an orderfor switching a short TTI length to long TTI length or vice versa.
 11. AUser Equipment (UE) for synchronized switching of a Transmission TimeInterval (TTI) between at least two different TTI length values, the UEbeing configured to deploy an actual- and a different-TTI length value,the UE comprising: a processing circuit comprising a processorconfigured to process program instructions and a memory arranged tostore the program instructions and network parameters; and an interfacecircuit configured to communicate with a base station (BS); wherein theprocessing circuit is configured to: receive, via the interface circuit,a switching message indicating that the UE is to switch from using TTIshaving a first length to using TTIs having a second length; and, inresponse to said switching message, switch from using TTIs having thefirst length to using TTIs having the second length, after apredetermined number of TTIs.
 12. The UE of claim 11, wherein theprocessing circuit is further configured to control the interfacecircuit to transmit a report comprising a measured received power, andwherein the switching message is received in response to the report. 13.The UE of claim 11, processing circuit is further configured to controlthe interface circuit to receive, prior to receiving the switchingmessage, a network parameter indicating an applicable number of TTIsafter which a switching of TTI length is to occur, and wherein thepredetermined number of TTIs is the indicated applicable number of TTIs.14. The UE of claim 11, wherein the processing circuit is configured toreceive the switching message via the secondary carrier when the UE isconfigured with multiple carriers in the downlink transmission and whenat least two carriers, a primary carrier and the secondary carrier, areactivated.
 15. The UE of claim 11, wherein the switching message sent bya serving High Speed Downlink Shared Channel (HS-DSCH) cell or asecondary serving HS-DSCH cell, comprises a predetermined order mappingindicator indicating an order for switching a short TTI length to a longTTI length or vice versa.
 16. The UE of claim 11, wherein the processingcircuit is further configured to start a counter counting TTIs, thevalue of the counter indicating when transmission with the second TTIlength commences.
 17. A Base Station (BS) for synchronized switching ofa Transmission Time Interval (TTI) between at least two different TTIlength values, the BS comprising: a processing circuit comprising aprocessor configured to process program instructions and a memoryconfigured to store the program instructions and network parameters; andan interface circuit configured to communicate with one or more UserEquipments (UEs); wherein the processing circuit is configured to:receive a report message from a UE, the report message comprising ameasured received power; evaluate the report and decide, based on theevaluation, to order the UE to initialize a switching of an actual TTIlength value to a different TTI length value, by transmitting aswitching message indicating that the UE is to switch from using TTIshaving the first length to using TTIs having the second length; and,after transmitting the switching message, switch, for communicationswith the UE, from using TTIs having the first length to using Illshaving the second length, after a predetermined number of Ills.
 18. TheBS of claim 17, wherein the processing circuit is configured to send tothe UE, prior to transmitting the switching message, a network parameterindicating an applicable number of TTIs after which a switching of TTIlength is to occur, and wherein the predetermined number of TTIs is theindicated applicable number of TTIs.
 19. The BS of claim 17, wherein theprocessing circuit is configured to send the switching message via asecondary carrier, when the UE is configured with multiple carriers inthe downlink transmission and at least two carriers, a primary carrierand the secondary carrier, are activated.
 20. The BS of claim 17,wherein the switching message, sent by a serving High Speed DownlinkShared Channel (HS-DSCH) cell or a secondary serving HS-DSCH cell,comprises a predetermined order mapping indicator indicating an orderfor switching a short TTI length to long TTI length or vice versa.